In general, there are available, as an operating mechanism of a switchgear, one using a hydraulic operating force for large power and one using a spring operating force for middle/small output power. The former is referred to as “hydraulic operating mechanism” and the latter as “spring operating mechanism”. In recent years, the advancement of size reduction of an arc-extinguishing chamber of a gas-insulated circuit breaker which is a type of a switchgear allows fault current to be cut off with a smaller operating force, so that application of the spring operating mechanism becomes popular. However, a gas-insulated circuit breaker of extra high-voltage class requires high-speed operating capability called “2-cycle operation” that is capability of achieving cutoff within a time length corresponding to two-cycle time periods of alternating current. A conventional spring operating mechanism typically has operating capability equivalent to about 3-cycle operation, and it is not easy to realize the two-cycle cutoff capability due to poor responsiveness of a retention mechanism or retention control mechanism of a spring force.
A first type of conventional example of an operating mechanism of such a switchgear is disclosed in Japanese Patent Application Laid-Open Publication No. 2007-294363, the entire content of which is incorporated herein by reference. In operation mechanisms disclosed in this document, a force of a cutoff spring is retained by a retention mechanism constituted by a latch, O-prop (opening-hook lever), and a catch through an output lever. In this configuration, when a trip current is applied to a solenoid serving as a retention control mechanism, a plunger of the solenoid activates the catch to allow the engagement between the catch and prop to be released, which releases the engagement between the output lever and the latch to rotate the output lever to release the cutoff spring force, thereby achieving cutoff operation.
A second type of conventional example of the switchgear operating mechanism is disclosed in Japanese Patent No. 3497866, the entire content of which is incorporated herein by reference. In a spring operating mechanism disclosed in this document, a pull-out lever and a retention lever are provided for retaining a cutoff spring force. In this configuration, the retention lever is activated not by the cutoff spring force but by a force of an acceleration spring at the cutoff operation time so as to release the cutoff spring force.
There is known a spring operating mechanism disclosed in Japanese Patent Application Laid-Open Publication No. 2009-32560, the entire content of which is incorporated herein by reference, as a third conventional example of the operating mechanism of a switchgear. In the spring operating mechanism of this reference, a force of a cutoff spring is retained by a retention mechanism constituted by a latch, a ring, and a pull-off link mechanism through an output lever. In this configuration, when a trip current is applied to a solenoid, a plunger of the solenoid activates the pull-off link to allow the engagement between the output lever and the latch to be released, which rotates the output lever to release the cutoff spring force, thereby achieving cutoff operation.
In the first type of conventional example of the switchgear operating mechanism, operation for releasing the cutoff spring force (cutoff operation) is constituted by the following three steps: operation of the catch driven by excitation of the solenoid, operation of the O-prop, and operation of electrical contacts including the cutoff spring. The first type of conventional example is disclosed in the above-referenced Japanese Patent Application Laid-Open Publication No. 2007-294363. The operational relationship between the above components is illustrated in FIG. 15. The horizontal axis denotes time, and vertical axis denotes a stroke of each components. In FIG. 15, the lowermost curve represents the waveform of a trip current and, above this, the stroke of the catch is depicted. Above this, the strokes of the O-prop and the cutoff spring are depicted. The uppermost curve represents an energizing signal of the contact in an arc-extinguishing chamber of a gas-insulated circuit breaker.
Time length from the start of application of the trip current until the operation of the O-prop is started along with the operation of the catch is assumed to be T1. Time length from the start of operation of the O-prop to the start of operation of the cutoff spring is assumed to be T2. Time length from the start of operation of the cutoff spring until the cutoff spring reaches its contact opening point is assumed to be T3. Assuming that contact opening time period is T0,T0=T1+T2+T3  (1)is satisfied.
In order to realize 2-cycle operation, it is necessary to reduce contact opening time period T0 to a given value. Thus, in a typical spring operating mechanism, operations of the components from the catch to the cutoff spring, which occur after the trip current application, are not started simultaneously. That is, the catch operates to some degree to release the engagement between itself and the O-prop to thereby allow operation of the O-prop to be started, and the cutoff spring starts operating after the O-prop operates to some degree. Thus, a mechanism that-retains a cutoff spring force operates in a stepwise manner, so that it is necessary to reduce respective time lengths T1, T2, and T3 in order to reduce T0.
However, since the cutoff spring force is determined by the mass of a movable portion of the arc-extinguishing chamber, opening speed, and drive energy, there is a limit to a reduction of T3. With regard to T2, mass reduction of the O-prop and increase in a force (retention force) of retaining the cutoff spring force allow high-speed operation of the O-prop. However, when the retention force is increased, the size of the O-prop needs to be increased for strength, which limits the mass reduction of the O-prop. It follows that there occurs a limit in the improvement in operation speed relying on the increase in the retention force. Further, when the retention force is increased, a large force is applied to the engagement portion between the O-prop and the catch, so that there occurs a need to increase the size of the catch for strength and to provide a solenoid having a large electromagnetic power for activating the catch.
At present, an excitation method using a large-sized condenser is adopted for obtaining a large power of the solenoid. However, the upper limit value for a current value flowing to the solenoid is specified in the standard, so that there is a limit in the improvement in the output power of the solenoid. As described above, it is difficult to reduce the contact opening time period in the conventional spring operating mechanism.
Also in the second type of conventional example (disclosed in Japanese Patent No. 3497866), operation for releasing the cutoff spring force is constituted by the following three steps: operation of a pull-off hook driven by an electromagnet; simultaneous operation of a reset lever, acceleration spring, and a retention lever; and simultaneous operation of a pull-off lever and a cutoff spring. In this example, the direction of a retention force (pressuring force) of the cutoff spring is made substantially coincident with the rotation center of the retention lever, thereby reducing a force required for the operation of the retention lever.
Further, the speed of movement of the retention lever, which is included in the above second step, is made higher by the accelerating spring to thereby reduce the operation time period. However, it is physically difficult to reduce the operation time period of the second step to zero and, therefore, it is difficult to significantly reduce the entire contact opening time period, also in terms of the problems described in the first example.
Further, the direction of a pressuring force to a portion at which the pull-off lever and the retention lever are engaged with each other is made substantially coincident with the rotation center of the retention lever, so that when an external vibration is applied to the retention lever to force the same to vibrate, the pull-off lever is rotated in the cutoff operation direction, and the cutoff operating mechanism may start operating without a cutoff command.
Further, although not described in the above referenced Japanese Patent No. 3497866, it is just conceivable that the retention lever operates in the cutoff direction due to an impact force applied when the roller pushes aside the retention lever for reengagement in the closing operation to allow the cutoff operation to be started without a cutoff command. As described above, in the second example, it is difficult to significantly reduce the contact opening time period and it is likely that a retention state of the cutoff spring becomes unstable.
In the third conventional example (Japanese Patent Application Laid-Open Publication No. 2009-32560), when the solenoid is excited, the cutoff operation is completed by two operation steps: a first operation step in which the latch is directly driven through the pull-off lever and the pull-off link to release an engagement between the latch and the roller pin; and a second operation step in which the cutoff spring operates. With the configuration in which the cutoff operation can be completed by two operation steps, the cutoff operation time period can be reduced. This means that T2 is removed from the expression (1) representing the contact opening time period. However, a torque in the opposite direction to the pull-off direction of the latch is applied to the latch by the cutoff spring force from the time when the latch is driven to the time when the engagement between the latch and the roller pin is released. This prevents significant reduction of the cutoff operation time period.
Further, the latch, the pull-off lever, and the pull-off link move in a unified manner, so that the mass of a movable portion becomes large, preventing high-speed operation.
Further, a connection between the latch and the pull-off link and a connection between the pull-off link and the pull-off lever are made by a pin connection, so that a gap is formed between each of the connections, preventing high-speed response.
Further, the latch is returned to the closed-state position by the biasing force of the latch return spring immediately before completion of the closing operation. At this time, the latch and the pull-off link move in a unified manner to increase the mass of the movable portion. Thus, if the latch return spring force is insufficient, the return of the latch is delayed, which may cause failure in the closing operation. If the latch return spring force is made larger as a countermeasure against the above problem, it requires longer time period to achieve the contact opening.